Adjustable inductance



Sept. 19, 1939. N. P. CASE 2,173,084

ADJUSTABLE INDUCTANCE Filed March 51, 1937 FIG.2.

l6 l3 l4 l5 FIG. 7.

INVENTOR. NELSON P. 35

ATTORNEY.

Patented Sept. 19, 1939 UNITED STATES BEISSUED PATENT OFFICE ADJUSTABLEINDUCTANCE Nelson P. Case, Great Neck, N. Y., assignor to HazeltineCorporation, a corporation of Delaware Application March 31,

18 Claims.

This invention relates to adjustable inductance units which, while ofgeneral application, are especially adapted for use as tuning elementsin the resonant circuits of a high-frequency signaling system for tuningthe circuits over broad bands of frequencies.

In high-frequency signaling systems, it is generally desirable tomaintain the antiresonant impedances of the resonant circuits at or neartheir maximum values as they are tuned over their respective ranges offrequencies in order that high gain may be obtained under allconditions. When an adjustable condenser is utilized as a tuning elementof a tunable circuit, its capacitance becomes so large at thelow-frequency end of the tuning range that the L/C ratio and theantiresonant impedance of the circuit, and hence the gain, areappreciably reduced. vHowever, if fixed condensers and adjustableinductance tuning elements are utilized in such resonant circuits, ahigh antiresonant impedance may be obtained over the entire tuningrange.

Adjustable inductance units heretofore devised have been subject tovarious objections. In general, these units have been either of the typecomprising fixed windings and an associated adjustable shield or of thewell-known adjustable winding variometer type. Both of these typesordinarily are objectionable in that they' have relatively small rangesof inductance variation and the shield type also has relatively highpower factors. While units of the variometer type have usually been theleast objectionable in these respects, even they ordinarily have arelatively limited range of variation. For an adjustable reactanceelement suitable for tuning over a wide frequency range, such as thebroadcast band, a variation of approximately 9:1 is required. Further,in conventional inductance units of the variometer type, very closespacing between windings is required for units of moder-' ate inductanceand moderate dimensions, giving a large variation of distributedcapacitance and limiting the tuning range when such unit is used as atuning element of a resonant circuit. Moreover, inductance units of thevariometer type heretofore devised have been relatively complicated andotherwise mechanically objectionable.

It is an object of the present invention, therefore, to provide a noveland improved adjustable inductance unit having a wide range ofinductance variation.

It is a further object of the invention to pro- 1937, Serial No. 134,069

vide an adjustable inductance unit of the type described having one ormore of the following characteristics: simplicity, compactness,ruggedness, and ease of operation.

In accordance with the present invention, there is provided a compositeadjustable inductance unit which comprises a first winding meansproviding a first magnetic field of predetermined shape, intensity, andpolarity. A second winding means, interleaving with said first windingmeans and having a mean diameter equal to that of said first windingmeans, is arranged to pro vide a second magnetic field of substantiallythe same shape and intensity as, but of an opposite polarity to, that ofthe first-mentioned winding means. An adjusting means is provided forsubstantially rectilinearly moving the two winding means with respect toeach other. This relative movement is preferably from a first position,in which the two magnetic fields are substantially mutually exclusiveand a maximum inductance is provided by the unit, to a second position,in which the fields are substantially coincident, so that the field ofthe second winding means substantially neutralizes or cancels the fieldof the first-mentioned winding means and a minimum inductance of arelatively small value is provided by the unit.

In one approved embodiment of the invention, three windings areindividually disposed on three coaxial cylindrical forms. These formsare dimensioned for telescopic movement, one within the other two. Thewindings are so proportioned and arranged that the two windings on theouter and inner forms provide a first magnetic field as described above,and the winding on the intermediate form provides the second magneticfield. Preferably, the outer and inner forms are secured in relativelyfixed telescopic relation, and means are provided operativelyinterconnecting a control element and the intermediate form so thatequal adjustments of the control element over its range effect differentdisplacements of the intermediate form relative to the outer and innerforms to vary the total inductance of the unit as described above. Thismanner of control renders the unit especially adaptable for use as atuning element, in that equal adjustments of the control element may bemade to effect equal variations in the resonant frequency of a circuitin which the unit is used as a tuning element.

As used in this specification, the term mean diameter is used to denotethe effective diameter for purposes of inductance computation of windingsystems to which the term is applied, and thus it may apply to a singlelayer winding, a multilayer winding, or a multiwinding system.

For a better understanding of the invention, together with other andfurther objects thereof, reference is bad to the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a simplified circuit diagramillustrating one approved form of the present invention; Fig. 2 is alongitudinal sectional view of the windings of an inductance unit suchas is illustrated in Fig. 1, indicating the magnetic fields produced bythe windings; Figs. 3, 4, 5, and 6 are circuit diagrams illustratingvarious modified forms of the present invention; and Fig. 7 is a sideelevation of a composite coupling unit embodying the present inventionwith certain portions shown in longitudinal section and certain portionsbroken away.

Referring in detail to Figs. 1 and 2, the inductance unit of the presentinvention illustrated by these figures comprises a pair of coaxialhelical windings Ill and I I, disposed one within the other with anannular space therebetween, and an additional helical winding I2 coaxialwith, and adapted to be telescoped within the annular space between, thewindings I0 and II, the windings I0 and II and the winding I2 thus beinginterleaving. The cross sections of the windings may, of course, be ofany desired shape other than circular, as shown. The radial dimension ofthe annular space between the windings I0 and II is preferably a smallfraction of the mean diameter of the windings so that the magnetic fieldproduced jointly by the two windings I0 and II is of substantially thesame shape and intensity as that produced by the single winding I 2. Forthis purpose also, it is preferable that the di ameter of the wire usedfor the windings I0 and I I be small relative to the mean diameter ofthe windings.

In the arrangement of Fig. l, the winding I2 is wound in a directionopposite to that of the windings Ill and II so that the polarity of thefield of the winding I2 is opposite to that of the field of the othertwo windings. The windings I0 and II are connected in parallel and thewinding I2 is connected in series therewith. The three windings are soproportioned as to have substantially equal inductances so that thecurrent through the winding I2 divides equally between the windings I0and II. By virtue 0? this arrangement, as illustrated in Fig. 2, thewindings Ill and II jointly provide a first magnetic field of apredetermined shape, intensity, and polarity, while the winding I2provides a second magnetic field of substantially the same shape andintensity as,

. but of an opposite polarity to, that of the first L1L2 Li L2 (1) whereL is the total inductance of the unit; Ll, La,

and La are the self-inductances of the windings I0, II, and I2,respectively; M1 is the mutual inductance between the windings I0 and II and M2 is the mutual inductance between the pair of windings ID and IIand the winding I2. The dimensions of the unit are so related that themaximum value of 2M2 approaches that of the expressionas closely aspossible.

It will thus be seen that, with the winding I2 disposed in the positionin which the two fields are substantially mutually exclusive, there issubstantially no mutual inductance between the winding I2 and thewindings III and I I, the value of M2 is inappreciable or substantiallyzero. In this position, therefore, the total inductance of the unit is amaximum. On the other hand, when the winding I2 is disposed in thesecondmentioned position with the two fields substantially coincident,the mutual inductance M2 between the winding I2 and'the windings ID andII is a maximum and the total inductance of the unit is reduced to aminimum.

It will be noted that, in the arrangement 01 Fig. l, the high potentialend of the winding I2 is adjacent the high potential ends of thewindings Ill and II when the winding I2 is disposed within the other twowindings. By virtue of this arrangement, thediiferences in potential ofadjacent portions of the winding I2 and the other two windings is fairlysmall for all adjustments thereof and the variation of distributedcapacitance between these windings has only a'small effect on thecharacteristics of the unit. Care should be taken that the power factorsand impedances of the windings I0 and II are substantially equal at allfrequencies at which the unit is to be operated so that the currentthrough the two windings will be substantially equal under allconditions.

In Fig. 3 there is illustrated a modified form of the invention which isidentical with that shown in Fig. 1, except that all three of thewindings are wound in the same direction and the difference inpolarities of the two fields is obtained by reversing the connections ofthe winding I2. While, in certain cases, substantially satisfactoryresults may be obtained with this arrangement, when the windings arecompletely telescoped, the low potential end of winding I2 is oppositeto the high potential ends of the other two windings. so that thedistributed capacitance therebetween is somewhat more effective than inthe embodiment of Fig. 1.

In Figs. 4 and 5 two additional modified forms of the invention areillustrated which are similar to the embodiments of Figs. 1 and 3,respectively, except that all three of the windings are connected inseries and the several windings are of correspondingly differentrelative proportions. In Fig. 4 the difference in polarity of the twofields is obtained, as in Fig. 1, by winding the element oppositely tothe windings I6 and H. In Fig. 5, on the other hand, the difference inpolarity is obtained, as in Fig. 3, by reversing the connections of thewinding I2. In the embodiments of both Figs. 4 and 5, since all of thewindings are connected in series, the total inductance provided by theunit maybe according to the formula:

L'=L1+L2+2M1+L3 2M2 3) in which corresponding terms representthe samefactors as in Equation (1) In the embodiments of Figs- 4 and 5, also,the inductances of the windings I and II individually are preferablysubstantially equal, but, since the total inductance of these windings,L1+Lz+2M1, is approximately 4L1, the total inductance of the unit isTherefore, it is necessary that the inductance of the winding l2 beapproximately four times that of each of the windings l0 and II in orderthat the total inductance may be reduced to approximately zero when thetwo fields are substantially coincident or M2 is at its greatest value.

In Fig. 6still another modified form of the invention is illustrated.Here, the three windings are all connected in parallel with the windingl2 wound in a direction opposite to that of the windings I0 and II inorder to obtain the desired difference in polarity of the two fields. Inthis case, the winding I2 preferably has a self-inductance approximatelyequal to that of each of the windings I0 and II in order that the totalinductance of the unit may be varied from its maximum value to a minimumvalue of approximately zero.

-The inductance of the unit of Fig. 6 may be determined according to theformula:

in which corresponding terms represent the same factors as in the otherequations.

If then, L1 L2 L3=Ml=M2 Ll where unity 4 coupling between L1 and In isassumed, then for the minimum total inductance of the unit the followingequation holds:

and for the maximum total inductance for the unit, where M 2:0, thefollowing equation holds:

' LIZ L! L max.= ,M (6) It will be noted that this embodiment has thespecial advantage that the effect of the distribuuted capacitance isreduced to a minimum, since, when the windings are completelytelescoped, there is no difference in potentials between adjacent partsof the windings.

Referring to Fig. 7, there is illustrated a physical construction of aninductance unit embodying the present invention. This unit comprisesthree coaxial cylindrical forms l3, II, and IS on which are disposed thewindings III, II, and 12, respectively. The form It is disposed withinthe form I3, leaving an annular space therebetween and these two formsare rigidly secured to a suitable base l6, as shown. The form I5 is of adiameter intermediate between the diameters of the forms l3 and I4 andis adapted to be telescoped therebetween. An end piece I! is secured tothe end of the form l5 remote from the base l6 and is provided withguide passages l8 and I9. There is also provided a fixed support 20having transverse openings 2| and 22 corresponding to the openings l8and I9, respectively, in the end piece IT. A guide rod 23 is rigidlysecured in the opening 2| parallel to the common axis of the forms andextends through the passage I8 to prevent rotation of the form l5 whileguiding axial movements thereof. A shaft 24 extends through the opening22 and passage l9 and is provided with a suitable actuating knob 25 andannular collars 25 to prevent longitudinal movement thereof. A spiralscrew thread 21, of a pitch gradually increasing in the direction of thesupport 20, is formed in the shaft 24 and engages a pin 28 in the endpiece ll. This shaft and pin arrangement thus provides a nonuniformmotiontransmitting means connecting the control element or knob 25 andthe intermediate form. The windings H), H, and I2 may be proportioned,arranged, and connected in accordance with the embodiments illustratedin any of Figs. 1, 3, 4, 5 or 6.

In the operation of the inductance unit of Fig. '7 to adjust theinductance thereof, the knob 25 is rotated to rotate the shaft 24 and,because of the engagement of the pin 28 in the screw thread 21, the formI5 is axially moved relative to the forms l3 and M. The limits ofmovement of the form 85 are from its innermost position where the fieldsdeveloped by the windings are substantially coincident and the totalinductance of the unit is a minimum, to a position external to the formsl3 and H where the magnetic fields in question are substantiallymutually exclusive and the total inductance of the unit is a maximum.The forms are so proportioned that the radial dimension of the annularspace between the forms l3 and I4 is a small fraction of the meandiameters of these forms. By virtue of this arrangement, the magneticfields produced jointly by the windings on these two forms is ofsubstantially the same shape and intensity as that produced by thewinding on the form l5 and when the form i5 is telescopically moved toits position between the other forms, the two fields are substantiallycoincident. It will be apparent that this result is not obtainable by aunit including only two telescopically engaging windings since, inasmuchas one of such windings must have a lesser diameter than the other inorder to obtain telescopic engagement, the two fields will necessarilybe of difierent shapes rendering coincident positioning thereofimpossible. Due to the variation in the pitch of the screw thread 21,equal adjustments of the knob 25 from the first to the second extremepositions mentioned above effect gradually increasing adjustments of thewinding 12. A unit of the type described is especially well adapted'foruse as a tuning element in a resonant circuit since, with the pitch ofthe screw thread varying in a proper manner, equal adjustments of theknob 25 effect the proper adjustments of the total inductance of theunit to impart to the unit a straight-line frequency characteristic overits entire tuning range.

While there have been described what are :at present considered thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from this invention, including various othermanners of connecting and positioning the windings of the unit inaddition to those described in detail, and, therefore, it is aimed inthe appended claims to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

What is claimed is:

1. A composite adjustable inductance unit comprising afirst windingmeans providing a and polarity, a second winding means interleaving withsaid first winding means and having a mean diameter equal to that ofsaid first winding means and providing a magnetic field coaxial with, ofsubstantially the same shape and intensity as, but of an oppositepolarity to, that of said first means, and means for relatively axiallymoving said two Winding means.

2. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of predetermined shape, intensity, andpolarity, a second winding means interleaving with said first windingmeans and having' a mean diameter equal to that of said first windingmeans and providing a magnetic field coaxial with, of substantially thesame shape and intensity as, but of an opposite polarity to, that ofsaid first means, and means forrelatively axially moving said twowinding means from a first position in which said fields aresubstantially mutually exclusive to provide a maximum inductance to asecond position in which said fields substantially coincide to provide aminimum inductance.

3. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of predetermined shape, intensity, andpolarity, a second winding means interleaving with said first windingmeans and having a mean diameter equal to that of said first Windingmeans and providing a magnetic field coaxial with, of substantially thesame shape and intensity as, but of an opposite polarity to, that ofsaid first means, adjusting meansior relatively axially moving said twowinding means, control means for said adjusting means, and nonuniformmotion-transmitting means connecting said control means and saidadjusting means whereby equal adjustments of the former over its rangeof adjustment effect predetermined difierent relative movements of saidwinding means.

4. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of predetermined shape, intensity, andpolarity, a second winding means interleaving with said first windingmeans and having a mean diameter equal to that of said first windingmeans and providing a magnetic field of substantially the same shape andintensity as, but of an opposite polarity to, that of said first means,adjusting means for relatively movingsaid two winding means whilemaintaining the polarities of said fields substantially unchanged from afirst position with the fields of said two winding means substantiallymutually exclusive to a second position with the fields of said windingmeans substantially coincident, control means for said adjusting .means,and nonuniform motion-transmitting means so connecting said controlmeans and adjusting means that equal adjustments of said control meanseffect gradually decreasing relative movements as said windings aremoved from said first position to said second position.

5. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of predetermined shape, intensity,andpolarity, a second winding means interleaving with said first windingmeans and having a mean diameter equal to that of 'said first windingmeans and providing a magnetic field of the same shape and intensity as,but of an opposite polarity to, that of said first means, said two iwinding means being coaxially disposed and dimensioned for telescopicmovement, and means for relatively axially moving said winding means.

6. A composite adjustable inductance unit comprising a pair ofrelatively fixed windings providing a magnetic field of a predeterminedshape, intensity, and polarity, an additional winding interleaving withsaid pair of windings and having a diameter equal to the mean diameteror" said pair of windings and providing a magnetic field ofsubstantially the same shape and intensity as, but of an oppositepolarity to, that of said pair of windings, and means for axially movingsaid pair of windings and. said ad'- ditional winding relative to eachother.

7. A composite adjustable inductance, unit comprising a pair ofrelatively fixed coaxial windings one disposed within the other, anadditional winding interleaving with said pair of windings and having adiameter equal to the mean diameter of said pair of windings andcoaxially disposed with respect to said pair of windings and dimensionedfor telescopic movement therebetween, and means for telescopicallymoving said pair of windings and said additional winding relative toeach other from a substantially mutually exclusive position to providemaximum inductance to a position with said additional winding telescopedbetween the windings of said pair to provide minimum inductance.

8. A composite adjustable inductance unit comprising a pair of coaxialwindings disposed one within the other and providing an annular spacetherebetween of a radial dimension which is a small fraction of the meandiameter of said windings, an additional winding coaxial with, andinterleaving with, said pair of windings and dimensioned for telescopicmovement therebetween, and means for relatively telescopically movingsaid pair of windings and said additional winding from a substantiallymutually exclusive position providing maximum inductance to a positionwith said additional winding disposed in said annular space to provideminimum inductance.

9. A composite adjustable inductance unit comprising a first windingmeans, a second interleaving winding means, said two winding meanshaving the same mean diameter and being coaxially disposed anddimensioned for telescopic engagement, and means for axially moving saidtwo winding means, relative to each other, from. a first position withsaid two winding means substantially mutually exclusive to provide amaximum inductance, to a second position with said two winding meanstelescopically disposed to provide a minimum inductance, the highpotential ends of both winding means being substantially adjacent in thelast-mentioned position.

10. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of a predetermined shape, intensity,and polarity, a second winding means interleaving with said firstwinding means and having a mean diameter equal to that of said firstwinding means and connected in series with said first means, said twowinding means providing a magnetic field coaxial with, of substantiallythe same shape and intensity as, but of an opposite polarity to, that ofsaid first means, and means for relatively axially moving said twowinding means.

11. A composite adjustable inductance unit comprising a first windingmeans providing a magnetic field of predetermined shape, intensity, andpolarity, a second winding means interleaving with said first windingmeans and having a mean diameter equal to that of said first windingmeans and connected in parallel with said first means, said two windingmeans providing a magnetic field coaxial with, of substantially the sameshape and intensity as, but of an opposite polarity to, that of saidfirst means, and means for relatively axially moving said two windingmeans.

12. A composite adjustable inductance unit comprising a pair of windingsconnected in parallel and arranged to provide a magnetic field of apredetermined shape, intensity, and polarity, an additional interleavingwinding connected in series with the windings of said pair and arrangedto provide a magnetic field coaxiaLwith. of substantially the same shapeand intensity as, but of a polarity opposite to, that of said pair ofwindings, and means for relatively axially moving said pair of windingsand said additional winding.

13, A composite adjustable inductance unit comprising a pair ofconcentric windings connected in parallel and providing a magnetic fieldof predetermined polarity, an additional interleaving winding connectedin series and concentric with the windings of said pair and providing a,magnetic field coaxial with, but of a po-- larity opposite to, that ofthe first said field, all of said windings being proportioned to havesubstantially the same inductance, and means for relatively axiallymoving said pair of windings and said additional winding from positionswith said fields substantially mutually exclusive to positions with saidfields substantially coincident.

14. A composite adjustable inductance unit comprising a pair of windingsconnected in series and arranged to provide a magnetic field of apredetermined shape, intensity, and polarity, an additional windinginterleaving with said pair of windings and having a diameter equal tothe mean diameter of said pair of windings and connected in series withthe said pair of windings, said additional winding being arranged toprovide a magnetic field coaxial with, of substantially the same shapeand intensity as, but of a polarity opposite to, that of said pair ofwindings, and means for relatively axially moving said pair of windingsand said additional winding.

15. A composite adjustable inductance unit comprising a pair ofconcentric windings connected in series, having substantially equalinductances and providing a magnetic field of predetermined polarity, anadditional winding ini terieaving with said pair of windings and havinga diameter equal to the mean diameter of said pair of windings andconnected in series and concentric with the windings of said pair,having an inductance approximately four times that of each of thewindings of said pair and providing a second magnetic field coaxialwith, and of a polarity opposite to, that of the -first said field, andmeans for relatively axially moving said pair of windings and saidadditional winding from positions with said field substantially mutuallyexclusive to positions with said fields substantially coincident.

16. A composite adjustable inductance unit comprising three coaxialcylindrical forms adapted to be telescoped one within another, the innerand outer forms being relatively fixed and having a mean diameter equalto that of the other of said forms, a winding disposed on each of saidforms, said windings being connected in circuit and so dimensioned anddisposed that the windings on the outer and inner forms provide amagnetic field of predetermined shape, intensity, and polarity and thewinding on the intermediate form interleaves with the windings on theinner and outer forms and provides a magnetic field of substantially thesame shape and intensity as, but of an opposite polarity to, that ofsaid first field, and means for effectin relative movement between saidouter and inner forms and said intermediate form.

17. A composite adjustable inductance unit comprising three coaxialcylindrical forms adapted to be telescoped one within another, the innerand outer forms being relatively fixed and having a mean diameter equalto that of the other of said forms, a winding disposed on each of saidforms, said windings being connected in circuit and so dimensioned anddisposed that the windings on the outer and inneriorms provide amagnetic field of predetermined shape, intensity, and

polarity and the winding on the intermediate form interleaves with thewindings on the inner and outer forms and provides a magnetic field ofsubstantially the same shape and intensity as, but of an oppositepolarity to, that of said first field, a control element, and nonuniformmotiontransmitting means connecting said element to said intermediateform, whereby equal adjustments of said element over its range ofadjustment effect different movements of said intermediate form relativeto said outer and inner forms.

18. 'A composite adjustable inductance unit comprising three coaxialcylindrical forms adapted to 'be telescoped one within another, theinner and outer forms being relatively fixed and having a mean diameterequal to that of the other of said forms, a winding disposed on each ofsaid forms, said windings being connected in circuit and so dimensionedand disposed that the windings on the outer and inner forms provide amagnetic field of predetermined shape, intensity, and polarity and thewinding on the intermediate form interleaves with the windings on theinner and outer forms and provides a magnetic field of substantially thesame shape and intensity as, but of an opposite polarity to,

that of said first field, a control element, and

nonuniform motion-transmitting means so connecting said element and saidintermediate form that equal adjustments of said element over its rangeof adjustment effect gradually decreasing movements of said intermediateform relative to said outer and inner forms from a first positionsubstantially external to said outer and inner forms to a secondposition substantially completely telescoped therebetween.

NELSON P. CASE.

